OpenGL with SRgb color space no longer works in Qt6.4+ - qwidget

Question

I have an OpenGL application with a QWidget-based (no QtQuick/QML) Qt UI that I ported from Qt5 to Qt6. Most of it works fine, except that with Qt 6.4 and the Qt 6.5 beta (Qt up to 6.3 works fine!), the QSurfaceFormat color space setting no longer has an effect. I could not find any changes in the change log that should affect this. The only OpenGL-related change mentioned is to the RHI which shouldn't matter since I don't use QtQuick/QML.
In my main, before creating the QApplication instance I set up my default surface format and the Qt::AA_UseDesktopOpenGL attribute as follows:
auto surfaceFormat = QSurfaceFormat::defaultFormat();
surfaceFormat.setVersion(3, 3);
surfaceFormat.setProfile(QSurfaceFormat::CoreProfile);
surfaceFormat.setOption(QSurfaceFormat::DebugContext);
surfaceFormat.setColorSpace(QColorSpace::NamedColorSpace::SRgb);
surfaceFormat.setSamples(4);
QSurfaceFormat::setDefaultFormat(surfaceFormat);
QApplication::setAttribute(Qt::AA_UseDesktopOpenGL);
QApplication app(argc, argv);
In the constructor of my QOpenGLWidget-derived widget, I set a compatible texture format and the update mode:
setTextureFormat(GL_SRGB8_ALPHA8);
setUpdateBehavior(QOpenGLWidget::NoPartialUpdate);
In initializeGL I set up a QOpenGLDebugLogger and load my OpenGL functions using glad Using QOpenGLFunctions is not an option as that would imply making the rendering code Qt-dependent and/or require significant changes. I also tried outputting the name of the color space reported by the widget's surface format via qDebug() and it is "SRgb" as expected.
At the beginning of paintGL I ensure GL_FRAMEBUFFER_SRGB is enabled before drawing using glEnable(GL_FRAMEBUFFER_SRGB).
In summary, it works in Qt 5.13 to Qt 6.3.2, but stops working with Qt 6.4 (the 6.5 beta adds another bug where menus have a black background but it's a beta). I am not getting any relevant OpenGL debugger messages, just a lone performance warning due to a re-compiled shader. Am I doing something wrong that just happens to work on previous versions or is this a bug that none of the many Qt users have discovered over the course of more than one minor revision? Any ideas regarding resolutions / workarounds?